The present application generally relates to a bone anchoring device for the dynamic stabilization of bones, in particular for the dynamic stabilization of the spine, and in particular, to a bone anchoring element which can be connected with a flexible rod which has a smooth surface and which is made of an elastic material.
Bone anchoring devices comprising a bone screw and a flexible rod which is made of an elastic material are known from EP 1 364 622 A2 and EP 1 527 742 A1. The rod has a corrugated surface which cooperates with a rib structure provided on the bottom of the receiving part of the bone screw to form a form-fit connection. The bone anchoring device according to EP 1 527 742 A1 additionally comprises a closure element which has a rib structure engaging the corrugated surface of the rod. The positioning of the corrugated surfaces of the rod relative to the rib structure requires a precise insertion of the rod into the receiving part to avoid tilting. Furthermore, a continuous positioning is not possible. This makes the adjustment of the position of the rod relative to the receiving part difficult and time consuming.
US 2004/0138660 A1 discloses a locking cap assembly for locking a rigid rod to a receiving body of a bone screw. The locking cap assembly includes an inner and an outer locking element. The outer locking element is a nut-like member and the inner locking element is rotatably connected to the outer locking element. The inner locking element has on its side facing the rod a ring-shaped deformable contacting element which comes into contact with the rod. Upon tightening of the outer locking element, the deformable element is deformed which provides feed-back to the surgeon to allow him to determine whether the locking cap assembly is tightened to the required extent. In one example, the deformable element is a deformable metallic ring which becomes cold welded to the rod.
Based on the above, there is a need to provide a bone anchoring device which can be used with a flexible rod made of an elastic material and which has a convenient handling while simultaneously providing a safe locking.